This lets compositors avoid re-rendering the entire buffer when only the
outside of the squares changed.
If glfwGetBufferAge() returns 0 for any reason (the buffer was just
created, there was an error, or the underlying API doesn’t track buffer
age), we swap the entire buffer again.
This removes all dependencies from the GLFW test programs on the Vulkan
SDK.
It also removes support for linking the GLFW shared library (dynamic
library, DLL) against the Vulkan loader static library.
